1. Field of the Invention
In the field of reinforcing yarns and composites, the present invention relates to a process for the production of sized glass yarns, as well as to the yarns obtained and to the composites made from the said yarns.
2. Description of the Background
Reinforcing glass yarns are manufactured, in a known manner, from molten glass streams flowing through die orifices. These streams are drawn in the form of continuous filaments and these filaments are then assembled as base yarns, which are then collected.
Before being assembled in the form of yarns, the filaments are usually coated with a sizing composition by passing them through a sizing member. This deposition of sizing is very important: on the one hand, it allows the yarns to be obtained and, on the other hand, it allows these yarns to be used efficiently in the production of composites. Sizing has indeed the following usual functions: it protects the yarns from abrasion and thus prevents them from breaking during their manufacture and, possibly, during their use; it furthermore allows the combination of yarns with organic and/or inorganic materials, by facilitating, in particular, the wetting and/or impregnation of the yarns by these materials. In most cases, sizing also enhances the adhesion between the glass and the material to be reinforced and allows composites to be obtained with improved mechanical properties.
It is thus important for the deposition of sizing to be carried out efficiently and under the best possible conditions, so that the sizing can carry out its functions correctly.
The sizings most commonly used are aqueous sizings (containing more than 85% by weight of water) which are easy to deposit, the water then being removed by drying. Sizing compositions are normally chosen so as not to undergo chemical reactions at room temperature (during storage) and under the die (for example polymerization of the sizing, thereby making it impossible to deposit). On the other hand, they can optionally be chosen to polymerize under the effect of a treatment subsequent to the deposition on the filaments. This is, in general, a heat treatment at a temperature above 100.degree. C., carried out after collecting the yarns. This polymerization of the sizing makes it possible to obtain integral yarns (whose filaments are solidly attached to each other) and which can be manipulated, this integrity being especially desired in textile applications in which the yarns are subjected to high mechanical stresses.
Since each additional treatment of the sized yarns, in particular each energy-consuming treatment, results in additional cost with regard to the yarn manufacturing process and is liable to generate defects on the yarns obtained (problems of migration of the components of the sizing on a winding of heat-treated yarns, for example), it is economically advantageous to find means for reducing the importance or number of these treatments.
However, no process currently exists which is both very cost-effective (especially insofar as it does not require an expensive energy treatment of the sized yarns during their manufacture) and which makes it possible to obtain, in good yields (in particular at high rates, with a limited level of breakage and with no variation in the quality of the yarns which would necessitate rejection of some of the products), an entire range of sized yarns for various applications, these sized yarns having uniform coating and characteristics over their entire length.